Which transitional word is best used to indicate difference?

It must first be understood that transitional words are used in written and spoken communication as a means to allow a reader, or an audience, to follow the intended message of the communicator throughout the words and sentence structures that are used to achieve that communication. Basically, they are like gears that lead a reader, or an audience in the correct pathway to comprehend the full message that the writer, or speaker, intended to convey.

As such, there are a great many types of transitional words and their purpose is precisely that, to allow a reader to transition and follow the concepts communicated in a correct manner. In the case of contrast, or difference as the question here requests, the idea is to look for transitional words that allow a reader to understand that there will be a contrast, or an exposure of differences between ideas, or concepts, and one word that will help a reader to understand this would be: HOWEVER. A similar one to it, and used much as a synonym is BUT.